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Old 11-22-2015, 09:12 PM   #5
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Join Date: Mar 2013
Location: Sacramento CA
Posts: 105
Re: 89 Suburban - leaking TH400 transmission

I installed a brand new plastic kickdown switch with the correct O-ring. Put some white grease on the O-ring, then clicked it in.

I reinstalled the pan just finger-tight today, will wait for the gasket sealer to cure before torquing it to specs.

My conclusion at this point: the new plastic kickdown switch clicked in very snugly, unlike the old, worn out kickdown switch. I think that over the last 25 plus years, that plastic piece actually shrunk, thus causing the leak. It is an unbelievably poor design . .. over time, that plastic piece is guaranteed to cause a leak. Maybe mine will be good for the next 10 years . ..

I also loosened the screw in the vacuum modulator on the right/pass side of the trans. I understand this should allow the trans to shift a bit earlier.

Tomorrow I will tighten the pan to specs, add fluid, and test drive. Wish me luck, and thanks for the help!
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